1. Field of the Disclosure
The present invention relates to a liquid crystal display device, more particularly, to a touch panel embedded liquid crystal display device that is able to allow soft touch and to recognize touch stably, regardless of intensity of illumination such as external lights, reflected lights and the like.
2. Discussion of the Related Art
Recently display technology for presenting electric information signal visibly has been developed rapidly and various thinner and lighter flat display devices having excellent power consumption efficiency have been developed correspondingly only to be replaced with cathode ray tube (CRT) devices.
Such a flat display devices may include a liquid crystal display (LCD), plasma display panel (PDP), field emission display (FED) and electro-luminescent display device (ELD) device and the like.
Such flat display devices typically include flat display panels capable of presenting images. Such flat display panels generally include a pair of transparent insulation substrates having a luminescent or planarizing material provided there between. Among such flat display devices, liquid crystal displays control light permittivity using an electric field to display images. For that, an LCD device includes a display panel having a liquid crystal between two transparent substrates, a backlight unit emitting a light to the display panel and a driving circuit for driving the backlight unit and the liquid crystal.
In a liquid crystal display device, a display panel generally has plural unit pixel regions defined by plural gate lines and data lines that cross to form a matrix. A thin film transistor array substrate and a color filter array substrate face each other with a space provided between the two substrates to form a uniform cell gap. A liquid crystal is provided in the cell gap in each of the unit pixel regions.
The thin film transistor array substrate includes the gate and data lines, a thin film transistor formed at each cross portion between the gate and data lines as switching device, a pixel electrode at each unit pixel region or cell to be connected to the thin film transistor, and an alignment layer coated on the above elements. The gate and data lines receive signals from the driving circuits via pad parts for them, respectively.
Each thin film transistor responds to a scan signal supplied to the gate line and supplies a pixel voltage signal supplied to the data line to the pixel electrode for a given unit pixel region.
The color filter array substrate includes color filters formed to correspond to unit pixel regions, a black matrix for isolating the color filters and for reflecting external light, a common electrode for supplying a reference voltage to the unit pixel regions commonly, and an alignment layer coated on the above elements.
The thin film transistor substrate and the color filter array substrate are usually fabricated independently and then aligned and attached to each other. After that, liquid crystal may be provided after attachment by injection or before attachment using a “one drop fill” (ODF) technique.
In this example, the liquid crystal display device may include a passive light emitting diode that may control brightness of a screen by using a light emitted from the backlight unit arranged in a backside of the liquid crystal panel.
Technology of attaching a touch screen panel to such the liquid crystal display device has been suggested recently. A touch screen panel is a user interface typically attached to a display device to sense a corresponding touch point by changing an electrical characteristic at a point touched by opaque material, such as a user's finger or pen. When the user's finger or touch pen touches the screen, a touch panel attached to the liquid crystal display device can detect the corresponding touch point information based on the detected information.
The above-described liquid crystal display device with touch panel has several disadvantages: increased cost because of the touch screen panel, decreased yield because of additional process to attach the touch screen panel to the liquid crystal panel, reduced brightness and increased liquid crystal panel thickness.
In another configuration, a photo-sensor may be provided in the display to control the backlight unit based on brightness of external light. Also, some designs have not attached the touch panel to an outside of the display panel, but such design increases the volume of the display panel.
As follows, a conventional liquid crystal display (LCD) device will be described.
FIG. 1 is a sectional view schematically illustrating an LCD device including a conventional photo-type touch panel.
As shown in FIG. 1, an LCD device having a conventional photo-sensing type touch panel embedded therein includes a liquid crystal panel 10 including a first substrate 1, a second substrate 2, a pixel TFT 3 and a sensor TFT 4 and a backlight unit 20 provided under the liquid crystal panel 10 to transmit a light to the liquid crystal panel 10.
Here, according to the photo-sensing, light is emitted through the liquid crystal panel from the backlight unit 20, and the emitted light is reflected toward the liquid crystal panel when a user's finger or a predetermined material 30 touches the liquid crystal panel, to be sensed by the sensor TFT 4.
However, such conventional photo-sensing type touch panel embedded liquid crystal display (LCD) device recognizes touch based on reflection angle of external light, and thus touch sensitivity may be different according to the luminance of the external light. For example, if difference of the amount of light between the external light and an area shaded by touch is none or too little, it is difficult to sense touch.
The above conventional touch panel in-cell type LCD device thus may have following disadvantages.
First, according to the conventional touch panel embedded LCD device, external light as well as the light reflected from the backlight may be recognized. As a result, the sensor may fail to recognize the input signal precisely if the illumination intensity of the reflected light is similar to that of the external light.
Furthermore, as the output signal according to touch is different according to external environment, developing an algorithm for touch point recognition may be complicated. That is, if the external light is higher than the reflected light, the touch signal is may have a voltage lower than voltages of the other area. If the external light is lower than the reflected light, the touch signal is output with a higher voltage than voltages of the other area. As a result, it may be difficult to recognize an actual touch signal. For example, of the external environment has a strong luminance, a shadow may be recognized as touch even though the user's finger is not touching the panel.